API change

- Created `this.queue()` to accept requests into a FIFO queue
- Added `queue` node to `config.json`
- Extended `this.status()` to contain `queue` information
- Created `this.queueStatus()` and wired it to `/queue/:item` (enabled by config)
- Created `this.url()` to construct the full requested URL
- Created `this.mode()` to process `this.requestQueue.items`